This invention relates to a control device for a vehicular AC generator and a method of controlling the same, and more particularly to such a control device and method by which the battery can be charged quickly when necessary.
FIG. 7 is a circuit diagram showing a conventional control device for a vehicular AC generator, which is disclosed, for example, in Japanese Utility Model Publication (Kokoku) No. 62-30480. The circuit of FIG. 7 includes an AC generator 1, a full-wave rectifier 2 for rectifying the output of the AC generator 1, and a voltage regulator 3 for regulating the output voltage of the AC generator 1 to several distinct predetermined levels in accordance with the operation condition. The target voltage to which the voltage regulator 3 regulates the output voltage the AC generator 1 is adjusted to two distinct target levels in accordance with the output of an engine control unit 4. Further, the target voltage is adjusted to a third level when the battery terminal voltage detector terminal A is disconnected from the battery 5.
The AC generator 1 includes a three-phase armature coil 101 mounted on the stator (not shown) of the AC generator 1, and a field coil 102 mounted on the rotor (not shown) of the AC generator 1. The full-wave rectifier 2 coupled to the output of the three-phase armature coil 101 consisting of six main and three auxiliary diodes includes a main rectifier output terminal 201, an auxiliary output terminal 202, and a grounded terminal 203.
The voltage regulator 3 coupled to the auxiliary output terminal 202 and the field coil 102 includes a first series of voltage divider resistors 301, 302, and 303 coupled across the battery terminal voltage detector terminal A and the ground, and a second series of voltage divider resistors 304 and 305 coupled across the auxiliary output terminal 202 and the ground. The voltage divider resistors 301, 302, and 303 constitute the first voltage detector circuit and the voltage divider resistors 304 and 305 constitute the second voltage detector circuit. The junction point J1 of the first voltage divider resistors 301, 302, and 303 and the junction point J2 of the second voltage divider resistors 304 and 305 are coupled, through a zener diode 306 and a diode 307 and a diode 308, respectively, to the base of a controlling transistor 309, which is coupled in series with a resistor 311 across the auxiliary output terminal 202 and the ground. The collector of the controlling transistor 309 is coupled to the base of a power transistor 310 coupled in series with a surge absorber diode 312 across the auxiliary output terminal 202 and the ground. Further, a short-circuiting transistor 313 is coupled across the two terminals of the voltage divider resistor 303. The target voltage change-over terminal B of the engine control unit 4 is coupled to the auxiliary output terminal 202 through a resistor 314 and to the base of the short-circuiting transistor 313.
The engine control unit 4 includes a control transistor 401, the base of which is coupled to a control signal representing, for example, the vehicle speed, idling state, and the battery voltage. A serial connection of a key switch 6 and a charging state display lamp 7 is coupled across the battery 5 and the auxiliary output terminal 202 of the full-wave rectifier 2. Further, an electric load 8 is coupled across the main rectifier output terminal 201 and the ground through a load switch 9. The battery 5 is coupled across the main rectifier output terminal 201 and the ground.
Normally (i.e., if the battery terminal voltage detector terminal A is not disconnected), the voltage regulator 3 regulates the output voltage of the AC generator 1 to two distinct target voltage levels in accordance with the output of the engine control unit 4. When the control transistor 401 of the engine control unit 4 is turned off and hence the voltage at the target voltage change-over terminal B is at the high level H, the short-circuiting transistor 313 is turned on to short-circuit the voltage divider resistor 303, the voltage is controlled to the normal target level (e.g., 14.4 V) determined by the resistance ratio of resistor 302 with respect to the sum of the resistors 301 and 302. When, on the other hand, the control transistor 401 of the engine control unit 4 is turned on and hence the voltage at the target voltage change-over terminal B is at the low level L, the voltage is controlled to the reduced target level (e.g., 12.8 V) determined by the resistance ratio of the resistors 301 through 303. More particularly, the reduced target level is determined by the resistance ratio of the serial connection of the resistors 302 and 303 with respect to the serial connection of the resistors 301, 302 and 303. Next, the operation of the circuit is described in greater detail.
When the key switch 6 is closed to start the engine, the base current is supplied from the battery 5 to the power transistor 310 through the key switch 6, the charging state display lamp 7, and the resistor 311. The power transistor 310 is thus turned on, such that the field current is supplied from the battery 5 to the field coil 102 through the key switch 6 and the charging state display lamp 7. Thus, the charging state display lamp 7 is turned on to indicate that the battery 5 is not currently charged. At the same time, the base current is supplied to the short-circuiting transistor 313 from the battery 5 through the resistor 314. The short-circuiting transistor 313 is thus turned on, to short-circuit the voltage divider resistor 303. Thus, the first voltage detector circuit is constituted only of the voltage divider resistors 301 and 302.
When the engine is started under this circumstance, an AC voltage corresponding to the rpm of the engine is induced across the three-phase armature coil 101, and the output of the AC generator 1 is full-wave rectified by the full-wave rectifier 2. Assume that the full-wave rectified output voltage of the AC generator 1 is still less than a predetermined level, 14.4 V, and that the control transistor 401 of the engine control unit 4 is turned off and hence the voltage at the target voltage change-over terminal B is at the high level H. Then the voltage at the junction point J1 is still insufficient to cause the break-down of the zener diode 306, and hence the zener diode 306 is kept turned off. The controlling transistor 309 is thus also kept turned off, and the power transistor 310 continues to be turned on to supply the field current to the field coil 102. As the rpm of the AC generator 1 increases with the increase of the rpm of the engine, the output voltage thereof rises. When the output voltage of the AC generator 1 thus exceeds the predetermined level, 14.4 V, the voltage at the junction point J1 rises above the level to cause the break-down of the zener diode 306. The zener diode 306 is thus turned on, thereby turning on the controlling transistor 309. The power transistor 310 is thus turned off. The supply of the current to the field coil 102 is thus interrupted, to reduce the output voltage of the AC generator 1. When the output voltage level of the AC generator 1 falls to or below the predetermined level, 14.4 V, the zener diode 306 and hence the controlling transistor 309 are again turned off, thereby turning on the power transistor 310. The supply of the field current to the field coil 102 is resumed, to raise the output voltage of the AC generator 1.
By repeating the above operations, the output of the AC generator 1 is controlled to the predetermined normal target level, 14.4 V. The battery 5 is charged by the output of the AC generator 1 and the electric load 8 is supplied with power. When the voltage across the battery 5 thus rises to a level substantially equal to the output voltage of the AC generator 1 supplied from the auxiliary output terminal 202, the charging state display lamp 7 is turned off to indicate that the charging of the battery 5 is now complete.
The base of the control transistor 401 of the engine control unit 4 receives a signal based on the information supplied from various sensors (e.g., the information upon the vehicle speed, the idling state, and the battery voltage). Thus, when the engine is under normal operating condition and not in the idling state, the base of the control transistor 401 is at the low level, and the control transistor 401 is turned off. The short-circuiting transistor 313 is thus turned on to short-circuit the voltage divider resistor 303. As a result, the output voltage of the AC generator 1 is controlled to the predetermined normal target level.
When, on the other hand, the engine control unit 4 determines, based on the information from various sensors, that the engine is in the idling state and the battery voltage is above a predetermined level, the control transistor 401 is turned on, to reduce the voltage at the target voltage change-over terminal B to the low level L. The short-circuiting transistor 313 is thus turned off, and the voltage at the junction point J1 now rises to a higher level determined by the resistors 301, 302 and 303. The regulation target voltage is thus adjusted to the reduced predetermined level, 12.8 V. When the engine is idling, the output voltage of the AC generator 1 is thus regulated to the reduced target level, to reduce the load upon the engine and to improve the mileage per gallon of the fuel of the vehicle.
Furthermore, when the battery terminal voltage detector terminal A is disconnected from the battery 5, the output voltage of the AC generator 1 is regulated to a quick-charging voltage, 15.6 V, determined by the voltage at the junction point J2 between the voltage divider resistors 304 and 305. The over-charging of the battery 5 is thereby prevented.
It is noted that the three target voltage levels are determined by the resistance ratios of the resistors 301 through 305.
As described above, the above conventional control device for a vehicular AC generator controls the output voltage of the AC generator 1 to the normal level, 14.4 V under the normal operation condition. When the engine is in the idling state, however, the target voltage is switched to the reduced level lower than the normal. The mileage of the vehicle is thereby improved. However, in the case of the above conventional control device, even when a rapid charging of the battery is needed, no measure can be taken other than raising the target output voltage of the AC generator 1 from the reduced to the normal level. The quick charging capacity of the control device is thus insufficient.